Weyl-equivariant splitting conjecture for saturated covers

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Let G‾0\overline{G}_0 be a saturated cover, let XQ,n\mathscr{X}_{Q,n} be the relevant lattice, and let X0,Q,n\mathscr{X}_{0,Q,n} be the Weyl-stable sublattice. Let WW act by the usual Weyl action and let σX0\sigma_{\mathscr{X}_0} and σX\sigma_{\mathscr{X}} be the associated permutation representations. Weyl-equivariant splitting conjecture. There exists a WW-equivariant splitting s:XQ,nΓ→XQ,ns:\mathscr{X}_{Q,n}^\Gamma\to\mathscr{X}_{Q,n}. Consequently, for every z∈s(XQ,nΓ)z\in s(\mathscr{X}_{Q,n}^\Gamma), σX0,z≃σX0\sigma_{\mathscr{X}_0,z}\simeq\sigma_{\mathscr{X}_0} and σX=∣XQ,nΓ∣⋅σX0\sigma_{\mathscr{X}}=|\mathscr{X}_{Q,n}^\Gamma|\cdot\sigma_{\mathscr{X}_0}; in particular, the corresponding Whittaker dimensions satisfy

dim⁡Wh⁡ψ(πχ‾‾‾‾,S)=∣XQ,nΓ∣⋅dim⁡Wh⁡ψ(πχ‾‾‾‾0,S).\dim\operatorname{Wh}_\psi(\pi_{\overline{\overline{\overline{\overline{\chi}}}},S})=|\mathscr{X}_{Q,n}^\Gamma|\cdot\dim\operatorname{Wh}_\psi(\pi_{\overline{\overline{\overline{\overline{\chi}}}}_0,S}).

This conjecture would make the Weyl action compatible with the lattice splitting and yield the stated multiplicity formula for Whittaker models.

References

Primary source

Fan Gao, Freydoon Shahidi and Dani Szpruch, “Restrictions, L-parameters, and local coefficients for genuine representations”, arXiv:2102.08859 (2021).

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